A common misconception, even amongst scientists who should know better, is that evolution has direction. Biologists often speak of "higher" and "lower" organisms, as if some creatures are better than others. A biologist speaks this way, to differentiate between unicellular (or lower) eukaryotes such as yeast and multicellular (higher) eukaryotes like you and me. But are yeast really "lower" than humans?
The answer is no. Yeast are not lower than humans. For by what absolute (and it must be absolute and quantitative, not just qualitative) scale would you measure such a thing? By abundance? There are approximately 6.5 billion humans alive today; more yeast than that are needed to make a single batch of bread dough or a vat of beer. By complexity? On the face of it, a human appears more complex than a single yeast cell, but our genomes - our genetic makeup - is not that dissimilar. Some plants have more genetic material than humans: does that make them more complex, and thus "higher"? No, complexity is not suitably definable to be an absolute scale. And without an absolute scale, without some sort of ladder on which to place every single living thing, we cannot say that one thing is higher or lower than another.
Even consciousness is not a scale that one can apply across the board to determine higher from lower. Humans, most of us would agree, are conscious. Many agree that cetaceans - dolphins and whales - also have a certain degree of consciousness. So do our cousins the chimpanzees and other great apes. Such animals are probably self-aware, but not to the same level that we are. But what distinguishes a yeast from a plant? Which is higher, which lower, on a scale of consciousness? A plant can respond to sunlight, which is more than can be said for a yeast. Yet a yeast can move to get food: a plant is stationary. Such a ladder then would have humans above chimps and whales, and everything else lumped together at the bottom. A ladder with only three rungs doesn't get you very far. It really isn't very useful.
So we must discard the notion of direction in evolution. There is no higher and lower, no better or worse, no ladder. Darwin proposed a tree of life, with each organism being a mere twig. Trees grow towards where the sunlight is. Natural selection is the sunlight for descent with modification.
Evolution can be seen in the fossil record. One can place the skulls of chimpanzees to early hominids to modern humans in a line and call it progression. But progression from what, towards what? Evolution does play favorites (what else after all is natural selection?), it is only for short term gain. Natural selection favors those who are most able to survive and reproduce under the conditions that are prevailing at the time. If conditions change, what was selected before may no longer be a benefit. The organism must then either adapt to the new conditions (it must evolve) or it will go extinct. There is no devolution: it's all evolution. Evolution is change, and change is constant.
Perhaps the question that should have been posed is what selective pressures are being applied to the human race today? But, since that was not asked, I will leave the answer to a different essay.